Many consumer devices such as digital cameras (still and/or moving picture), digital music players/recorders (e.g. MP3 players), personal digital assistants (PDAs), mobile telephones, and the like are now constructed to generate and/or utilize digital data in increasingly large quantities. Portable digital cameras for still and/or moving pictures, for example, generate large amounts of digital data representing images. Each digital image may require up to several megabytes (MB) of data storage, and such storage must be available in the camera. As such, present digital consumer devices require specialized storage memory to accommodate the large quantities of digital data.
To provide for this type of data storage application, storage memory should be: (1) relatively low in cost for sufficient capacities of around 10 MB to 1 gigabyte (GB); (2) low in power consumption (e.g. <<1 Watt); (3) have relatively rugged physical characteristics to cope with the portable battery powered operating environment; (4) and should preferably have a short access time (ideally less than one millisecond) and moderate transfer rate (e.g. 20 Mb/s), yet be able to be packaged in an industry standard interface module, such as PCMCIA or Compact Flash card. The limitations of the current industry standard FLASH memory, such as high cost and relatively low capacity for broad utilization in the above described applications, are well known, and as such, recent advances have provided for a type of memory module termed “PIRM” (Portable Inexpensive Rugged Memory), which addresses the problem of low cost archival storage for digital camera and other portable appliances. The benefits of PIRM memory comport with the needs of high capacity memory in consumer devices above (e.g., an industry standard interface such as PCMCIA or Compact Flash, 2000 G shock tolerance, low power consumption (<<1W), short access time (<1 ms), moderate transfer rate (20 Mb/s), and sufficient capacity (10 MB-1 GB)). In addition, PIRM memory modules can offer lower cost by avoiding silicon substrates, by lowering areal density, and by minimizing process complexity.
However, production of PIRM memory modules can be problematic because popular consumer devices are requiring ever increasing amounts of such memory, and current production methods can be very expensive. This brings about the need for such exacting types of memory arrays to be produced on a mass scale in order to reduce costs.
Attempts have been made for such mass scale production by the patterning of thin films of metals and semiconductor on flexible plastic webs in a roll-to-roll production environment. However, plastic web production is currently plagued by deficiencies inherent in the actual patterning methods utilized on flexible substrates. Specifically, existing patterning solutions, such as screen print and ink jet, photolithography, and laser ablation each have deficits in resolution and/or throughput, and can also cause collateral damage. In particular, screen print or inkjet based patterning schemes yield a relatively low throughput and limited ability to pattern a wide range of materials that can be deposited. Photolithography, laser ablation, or other optically based patterning methods yield a relatively low throughput, higher capital cost, and low resolution. This is because the resolution of such optically based schemes is limited by diffraction in proportion to       λ    NA    ,where λ is the wavelength of the illumination and NA is the numerical aperture of the imaging system. Given that the depth of field for the imaging system, and hence its ability to deal with surface irregularities is limited by       λ          NA      2        ,at some point it becomes very difficult to resolve small features on a flexible substrate with such methodologies. This is because it is difficult to clamp a flexible substrate with a vacuum or electrostatic chuck without introducing surface irregularities, especially given the surface roughness typical of flexible webs.
Emboss and liftoff techniques can provide a low cost patterning method having a comparatively high resolution and high throughput when used on flexible substrates. However, several problems do limit its utility for producing electronics. One such limitation relates to the patterning of a multilayer deposition. The second such problem has to do with the performing of a second deposition/patterning step on top of a set of previously patterned films, as this process flow works well for a single homogeneous deposition, but not necessarily for heterogeneous depositions where multiple thin films are deposited in series and then co-patterned, because the sidewall coverage may produce shunts in the patterned features.
In an attempt to overcome such shortcomings, recent advances have been able to produce multiple layers, but even these advances are limited in that the developed processes are restricted to the usage of depositions which are spun on the rigid wafer substrate with the use of a photo resist, thereby relegating the process to less economical means which are limited in mass production potential.
Accordingly, prior art methodologies have been limited to the usage of the other previously described patterning methods, without consideration of the usage of embossing when patterning multiple films on flexible substrates.
As such, in order to adequately provide for digital circuitry such as PIRM memory modules, there is a need for the mass production, high definition, and the economies of scale which result from the utilization of the embossing process on flexible web sheet substrates when producing the required quantities amounts of cross point arrays and other types of related integrated circuitry.